This invention relates to a powder coating composition which is easy in handling, particularly in sieving.
Powder coating technology has become popular in finishing automobile bodies and parts, household electrical appliance and building materials because it does not use any organic solvent presenting environment pollution problems.
Powder coating compositions are generally produced by blending a binder resin with a curing agent and optionally other additives such as pigments, kneading the mixture under heat to make a molten mass, pulverizing solidified mass and then classifying the pulverized powder. The powder thus produced is applied onto a substrate using the electrostatic spray coating method or fluidized bed coating method to form a film, and then baked to form a cured film. The powder is sieved on site immediately before use to remove any agglomerated particles formed by blocking during transporting and storage. Portions of the powder not deposited onto the substrate are recovered and sieved to remove agglomerated particles and any particulate foreigh matter for recycling of recovered powder.
Solvent type coating compositions have been conventionally used in the field in which a highly aesthetic finish is critical. In order to use the powder coating composition in that field, the powder must have a volumetric average particle size as fine as from 5 to 20 .mu.m. However, the powder of a particle size in this range is not efficiently sievable not only in the classifying step of the powder as produced but also in the sieving step on site before or after the application onto the substrate because the powder tends to clog sieving screens more frequently than powder of larger particle sizes.
Therefore, a need exists for a powder coating composition which does not present the above problem in sieving.